The Symbolism of the American Flag is of revolutionary significance. Beginning with 13, the now 50 stars displayed in the canton of the flag represent the current number of states in the union. This number has followed the growth of the united-states since its infancy. Found from a book about the symbolism of the American Flag published in 1977 by the House of Representatives we read:
"The star is a symbol of the heavens and the divine goal to which man has aspired from time immemorial; the stripe is symbolic of the rays of light emanating from the sun."
Alternating in red and white, the 13 stripes also represent the 13 original colonies that joined together to declare their independence from Britain in order to establish themselves as a sovereign nation.
Originally, the colors red, white and blue had neither specific meaning nor representation when the flag was adopted in 1777. However, the colors in the Great Seal of the United States did have specific meanings. Charles Thompson, Secretary of the Continental Congress, reporting to Congress on the Seal, stated:
"The colors of the pales (the vertical stripes) are those used in the flag of the United States of America; White signifies purity and innocence, Red, hardiness & valor, and Blue, the color of the Chief (the broad band above the stripes) signifies vigilance, perseverance & justice."
More information on the Symbolism of the American Flag can be found here.